Collector for alkaline secondary battery, method for making the same, and alkaline secondary battery using the same

ABSTRACT

A hydrophilic collector for alkaline secondary batteries is formed of a nonwoven fabric plated with nickel in which the nonwoven fabric is hydrophilized by sulfonation, a gaseous fluorine treatment, or vinyl monomer grafting. A method for making the collector includes a hydrophilizing step of a nonwoven fabric comprising at least one of a polyolefin fiber and a polyamide fiber, and a plating step of applying nickel plating to the hydrophilic nonwoven fabric. Preferably, the nickel plating is electroless plating, and the nonwoven fabric has a plurality of micropores extending from one surface to the other surface thereof. An electroplating film may be deposited on the electroless plated film, if necessary. This collector facilitates assembling a battery which exhibits improved high-rate discharge characteristics due to improved adhesiveness of the plated nickel film to the nonwoven fabric.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 09/783,518 filedon Feb. 21, 2001.

The present application is based on Japanese application 2000-043017,filed on Feb. 21, 2000, and Japanese application 2001-002728, filed onJan. 10, 2001 which are both hereby incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a collector for alkaline secondarybatteries including a plated nonwoven fabric, to a method for making thesame, and to an alkaline secondary battery using the same.

2. Description of the Background

Alkaline secondary batteries, which are highly reliable and are suitablefor a reduction in weight, are widely used as power sources for variousdevices and apparatuses from portable devices to industrial largefacilities. In most alkaline secondary batteries, nickel electrodes areused as positive electrodes. A nickel electrode has a structureincluding a collector for collecting electricity and apositive-electrode active material inducing a cell reaction supported onthe collector. As collectors in this case, a sintered nickel plateformed by sintering nickel powder and a punched nickel plate have beenwidely used. The cell capacity is determined by the volume of the activematerial loaded in pores in such a nickel plate, and the volume of theloaded active material depends on the porosity of the nickel plate.Thus, it is preferable that the porosity of the nickel plate be as largeas possible.

However, in sintered nickel plates and punched nickel plates, theporosity is as low as 75% to 80%. Moreover, the nickel content in anitrate solution is low. Thus, the loading cycle for impregnation andneutralization must be repeated several times in order to load apredetermined amount of active material. Since the penetration of thenitrate solution into the interior of the nickel plate is impaired asthe loading cycle is repeated, high density loading of the activematerial is barely achieved. Recently, a collector with athree-dimensional network structure has been used in order to enhanceloading density of the active material into the collector to meet therequirements for higher capacity of batteries, since this structure haslarge porosity and thus can has high loading density for the activematerial.

The collector having the three-dimensional network structure isgenerally fabricated as follows. A porous network structure, such as apolyurethane foam sheet or an organic nonwoven fabric is plated withnickel by a known process, and is fired in a reducing atmosphere topyrolyze the polyurethane sheet or the fabric so that the plated nickelnetwork skeleton remains. In the resulting collector, a portion for anexternal terminal is flattened, the pores are filled with an activematerial paste, and a small nickel piece as an external terminal isspot-welded to the flattened position. Since the resulting collector haslarge pores and the porosity is as large as 90 to 98%, pasted nickelhydroxide can be directly loaded into the pores with high loadingdensity. This collector contributes to an increase in capacity ofalkaline secondary batteries.

However, this three-dimensional network structure does not have strengthrequired for the collector and is too rigid. Thus, producing anelectrode using this collector and assembling the electrode into abattery cause the following problems. When an active material paste withhigh viscosity is loaded into the collector, the active material pasteis injected from the surface into the internal pores of the collectorunder a predetermined pressure. After the loaded active material pasteis dried, the collector is rolled to increase the density and tooptimize the electrode thickness, and is cut into pieces with apredetermined size. When the pressure applied to the paste is increasedto improve the loading density of the paste, the nickel network skeletonof the collector may buckle or chip. Thus, the pressure on the activematerial paste must be reduced to avoid such buckling or chipping.However, desirable loading density of the paste is not achieved under alow pressure.

Since the nickel itself constituting the network skeleton is rigid, thenetwork skeleton will leave cracks and projections such as scuffing onthe outer periphery of the electrode using this collector, with chippingof the network skeleton in many cases, during winding the collector witha separator in the assembly of a cylindrical storage battery. Theseprojections increase the electrical resistance of the electrode andimpair the function of the collector and charge/dischargecharacteristics of the battery. In a prismatic storage battery usingthis collector, the collector swells due to a change in volume of theactive material during charge/discharge cycles in some cases. Hence,separation may occur between the collector and the active material, orin the active material, resulting in deterioration of charge/dischargecharacteristics due to deterioration of the collector itself.

In addition, this collector with three-dimensional network structure isproduced by many complicated steps with low productivity and relativelyhigh cost. Moreover, the metal, i.e., nickel, which is only theconstituent of the collector, precludes a decrease in thickness orweight of the collector. Accordingly, this metallic collector does notsufficiently meet the requirements for a decrease in weight and size.

In order to overcome this problem, Japanese Unexamined PatentApplication Publication No. 8-329956 discloses a collector having athree-dimensional network structure. In this collector, a polyurethanefoam sheet or a polyolefin nonwoven fabric is plated with nickel so asto impart conductivity to only the surface of the sheet or nonwovenfabric without pyrolyzing the sheet or nonwoven fabric. This collectorcan be produced by simpler steps, is flexible, and has relatively highstrength, in comparison with the above-mentioned pyrolyzed collectorwith a three-dimensional network structure. No crack or projectioncausing scuffing forms during winding an electrode using this substratetogether with a separator to assemble a cylindrical or prismaticbattery. This collector exhibits improved charge/dischargecharacteristics and can meet the requirement for a reduction in weightand size.

However, in this collector, adhesion is insufficient between thepolyurethane foam sheet or polyolefin nonwoven fabric and the platednickel. When this collector is used as a nickel electrode of anickel-hydrogen battery, the collector does not have a satisfactoryfunction in a combination with a nickel hydroxide active material. Thus,it is difficult to assemble high-capacity batteries.

Japanese Unexamined Patent Application Publication No. 5-290838discloses a method for making a nonwoven fabric electrode in which thenonwoven fabric is corona-treated prior to nickel plating. Thecorona-treated nonwoven fabric exhibits higher bonding strength to theplated layer compared to untreated nonwoven fabrics.

However, in this method, the bonding strength between the base materialand the plated layer is still insufficient in practice. When thiscollector is used as a nickel electrode in a nickel-hydrogen battery,the plated layer undergoes a change in quality or partial scaling duringassembling a battery and repeated charge/discharge cycles of thebattery. The resulting battery shows a short charge/discharge cycle lifeat high temperatures, resulting in an abrupt decrease in capacity.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide acollector for an alkaline secondary battery exhibiting improvedadhesiveness to plated nickel and a method for making the same.

It is another object of the present invention to provide an alkalinesecondary battery which can be easily assembled and exhibits a highdischarge rate and improved charge/discharge cycle characteristics.

According to a first aspect of the present invention, a collector for analkaline secondary battery comprises a nonwoven fabric hydrophilized bysulfonation, gaseous fluorine treatment, or vinyl monomer grafting, anda nickel plating film formed on the nonwoven fabric.

The nonwoven fabric hydrophilized by the above treatment has a uniformand fine negative charge over the entire region. In this collector, theplated nickel film is tightly bonded to the nonwoven fabric, improvingconductivity. Moreover, the plated nickel film does not scale off in usein an aqueous 20-35 weight % KOH solution, which is an electrolytegenerally used in alkaline secondary batteries, over a long period,preventing an increase in surface resistance.

Preferably, in this alkaline secondary battery, the nonwoven fabric hasa plurality of micropores extending from one surface to the othersurface thereof. A large amount of active material is thereby loadedinto the plurality of micropores, so that the alkaline secondary batteryhas high capacity.

Preferably, the diameter of the micropores is in the range of 0.1 to 5.0mm, and the micropore density (the number of micropores per area) in thenonwoven fabric is in the range of 1 to 30/cm². When the diameter isless than 0.1 mm or the micropore density is less than 1/cm², a requiredamount of active material is not loaded. When the diameter exceeds 5.0mm or the micropore density exceeds 30/cm², the nonwoven fabric cannotmaintain desired mechanical strength.

Preferably, the nonwoven fabric includes crimped fibers. Since thecrimped fibers are bulky, the nonwoven fabric has an increased porevolume, which can load an increased amount of active material.

Preferably, the nonwoven fabric is produced by a wet process. Thenonwoven fabric by the wet process is uniform with regard to weight andthickness, yielding a uniform electrode. Thus, an electrode with auniform thickness can be formed using this collector. When thiselectrode is wound, an electrode group having high adhesiveness isformed, and a battery using the wound electrode exhibits superiorcharge/discharge characteristics.

According to a second aspect of the present invention, a method formaking a collector for an alkaline secondary battery comprises ahydrophilizing step of a nonwoven fabric comprising at least one of apolyolefin fiber and a polyamide fiber, and a plating step of applyingnickel plating to the hydrophilic nonwoven fabric.

In this method, the hydrophobic polyolefin or polyamide fiber, whichprecludes penetration of an aqueous plating solution and nickel plating,is made hydrophilic. Thus, nickel ions are firmly affixed to the surfaceof the nonwoven fabric in a nickel plating treatment, the plated nickellayer tightly bonded to the nonwoven fabric. The resulting collectorexhibits high conductivity.

In this method, the hydrophilizing step preferably includes a treatmentselected from sulfonation, gaseous fluorine treating, and vinyl monomergrafting. The nonwoven fabric hydrophilized by the above treatment has auniform and fine negative charge over the entire region. In thiscollector, the plated nickel film is tightly bonded to the nonwovenfabric, improving its conductivity. Moreover, the plated nickel filmdoes not scale off in use in an aqueous 20-35 weight % KOH solution,which is an electrolyte generally used in alkaline secondary batteries,over a long period, preventing an increase in surface resistance.

Preferably, in this method, the nonwoven fabric has a plurality ofmicropores extending from one surface to the other surface thereof.

Since an active material is also loaded into the plurality ofmicropores, a large amount of active material is loaded so that thealkaline secondary battery has high capacity.

In this method, the nickel plating is preferably electroless plating.The electroless plating facilitates the formation of a plated nickelfilm an the nonconductive nonwoven fabric.

Preferably, the method further comprises a step of forming anelectroplating film by an electroplating process subsequent to theformation of an electroless plating film by the electroless plating.

Since the plated nickel film having a predetermined thickness is tightlybonded to the nonwoven fabric, the resulting collector has desiredconductivity.

According to a third aspect of the present invention, an alkalinesecondary battery comprises the collector according to the first aspector a collector manufactured by the method according to the secondaspect.

This alkaline secondary battery can be readily assembled using thecollector according to the first aspect or the collector manufactured bythe method according to the second aspect, and exhibits a, highdischarge rate and improved charge/discharge cycle characteristics dueto high adhesiveness of the collector to the plated nickel layer.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is an enlarged partial view of a collector including a nonwovenfabric and a plated film in accordance with the present invention;

FIG. 2 is an isometric partially broken-away view of an alkalinesecondary battery in accordance with the present invention;

FIG. 3 is a cross-sectional view taken from line 3—3 in FIG. 2, showinga spirally wound collector;

FIG. 4 is a cross-sectional view of a rectangular spiral collector; and

FIG. 5 is a cross-sectional view of a folded laminate collector.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be describedwith reference to the drawings.

With reference to FIG. 1, a collector 10 of the present inventionincludes a nonwoven fabric 11 composed at least one of a polyolefinfiber and a polyamide fiber, and a plated nickel film 12 provided on thesurface of the nonwoven fabric 11. Examples of the resin components ofthe polyolefin fiber include polyethylene, polypropylene,polymethylpentene, ethylene-propylene copolymers,ethylenebutene-propylene copolymers, and ethylene-vinyl alcoholcopolymers. Preferably, these resin components are used in combination.Examples of the resin components of the polyamide fiber include nylon-6,nylon-66, nylon-12, and copolymers of nylon-8 and nylon-12. Preferably,these resin components are used in combination.

The collector 10 is formed by hydrophilizing the nonwoven fabric 11 andby plating nickel on the hydrophilic nonwoven fabric 11. Polyolefinfibers and polyamide fibers have been used as separators of batteries.These fibers are resistant to alkali and are not dissolved into anaqueous 20-35 weight % KOH solution. Moreover, these fibers areavailable at low cost.

In the polyolefin fiber, polyethylene resin and polypropylene resin arepreferable due to high alkali resistance and acid resistance. Thepolyethylene resin and the polypropylene resin may be used alone or incombination. In particular, a core-sheath composite fiber of apolypropylene core and a polyethylene sheath simultaneously satisfyingalkali resistance and high strength is preferably used. Any fiber otherthan the polyolefin fiber and the polyamide fiber may be used as aconstituent of the nonwoven fabric in the present invention.

Preferably, the nonwoven fabric includes crimped fibers. The nonwovenfabric including the crimped fibers are bulky and have a large porevolume, which is advantageous to loading of an active material andbattery capacity. Moreover, loading of the active material isfacilitated by an increased average pore diameter. In the crimped fiber,the density of crimps is preferably 3/inch or more and more preferably5/inch or more. In order to maintain an adequate porosity, the nonwovenfabric contains the crimped fiber in an amount of preferably at least 5%by weight, more preferably at least 20% by weight, and most preferablyat least 50% by weight. The fibers may be mechanically or thermallycrimped. Examples of thermally crimpable fibers are side-by-side fibersand eccentric pore-sheath fibers which are composed of two types ofresins having different shrinking temperatures.

The nonwoven fabric may be fabricated by (1) a card or air lay process,(2) a dry process such as a melt-blown or spun-bond process, whichinvolves continuous formation of a sheet from a spinning stage, or (3) awet process dispersing fibers into water and making the nonwoven fabricfrom the dispersion. In particular, a nonwoven fabric fabricated by awet process has higher uniformity in the density and the thicknesscompared to a nonwoven fabric fabricated by a dry process. Thus, acollector using the wet-process nonwoven fabric provides an electrodewith a uniform thickness, and the electrode after winding provides anelectrode group having high adhesiveness. The resulting battery exhibitssuperior charge/discharge characteristics.

The porosity of the nonwoven fabric is preferably 70% or more. Herein,the porosity represents the proportion of the pores to the total volumeof the nonwoven fabric. A porosity of less than 70% causes a decreasedloading density of an active material paste and the resulting collector10 is not suitable for high-capacity batteries, regardless of highmechanical strength of the nonwoven fabric 11. A significantly highporosity results in a significant decrease in mechanical strength. Morepreferably, the porosity is in the range of 80 to 98%.

The nonwoven fabric 11, which is produced by the above process, may beused as it is. Preferably, the nonwoven fabric 11 is entangled andheat-treated to enhance mechanical strength prior to use. Examples ofentangling treatments are stream entangling, in which ultrafinehigh-pressure jet streams are impulsively applied, and needle punchentangling. As shown in FIG. 1, the entangled nonwoven fabric has manyjunction points 11 a between filaments and exhibits improved mechanicalstrength. Moreover, the entangled nonwoven fabric has a smallerthickness and a desirable porosity. The heat treatment is performed tolocally melt and bond the filaments at the junction points 11 a so as toenhance the overall mechanical strength. However, the heat treatmenttemperature must be below the pyrolyzing temperature of the fiber toprevent pyrolysis of the fiber.

The heat treatment is performed at a temperature between the softeningtemperature and the pyrolyzing temperature of the fiber. At asignificantly low temperature within the above range, the resultingnonwoven fabric exhibits low mechanical strength due to insufficient hotmelting, resulting in damage when an active material paste is loaded. Ata significantly high temperature, the porosity decreases due to the meltof the fibers, resulting in a decreased loading density of an activematerial paste. When the above-mentioned core-sheath composite fiber isused, the heat treating temperature is preferably in the range of 120°C. to 140° C. The entangling treatment and the heat treatment may beindependently performed. Preferably, the nonwoven fabric is entangledand is then heated to significantly improve mechanical strength thereof.

The present invention is characterized by hydrophilizing the surface ofthe nonwoven fabric. Since the polyolefin material such as polypropyleneis nonpolar, it precludes permeation of a plating solution and has pooradhesiveness. The above hydrophilizing treatment improves penetrabilityof a plating solution. Since nickel ions are firmly affixed to thenonwoven fabric, the nonwoven fabric exhibits high conductivity and theplated nickel layer is tightly bonded to then surface of the nonwovenfabric. The nonwoven fabric may be hydrophilized by sulfonation, gaseousfluorine treatment, vinyl monomer grafting, surfactant treatment orhydrophilic resin coating. Among these, sulfonation, gaseous fluorinetreatment, and vinyl monomer grafting are preferred, since thesetreatments do not cause scaling off of the plated metal film and anincrease in surface resistance in use over long time in an aqueous 20-35weight % KOH solution, which is used as an electrolyte solution inbatteries.

Sulfonation may be performed by immersion treatment using, for example,fuming sulfuric acid, sulfuric acid, sulfur trioxide, chlorosulfuricacid or sulfuryl chloride. Among these, sulfonation using fumingsulfuric acid is preferably due to high reactivity. Any gaseous fluorinetreatment may be effective in the present invention. For example, thenonwoven fabric may be exposed to a mixed gas of gaseous fluorinediluted with an inert gas such as nitrogen or argon, and at least onegas selected from oxygen, carbon dioxide and sulfur dioxide. When thenonwoven fabric is exposed to gaseous sulfur dioxide and then gaseousfluorine, the nonwoven fabric is effectively and permanentlyhydrophilized. Any vinyl monomer grafting treatment may be used in thepresent invention. For example, the nonwoven fabric is immersed in agrafting solution containing at least one monomer selected from acrylicacid, methacrylic acid, an acrylic ester, a methacrylic ester,vinylpyridine and styrene, and then is irradiated with ultraviolet rays.Among those monomers, acrylic acid is preferable since this monomer doesnot cause scaling off of the plated metal film and an increase insurface resistance in use over long time in an aqueous 20-35 weight %KOH solution, which is used as an electrolyte solution.

The resulting hydrophilic nonwoven fabric is subjected to nickelplating. Preferably, the nickel plating is electroless plating. Withreference to FIG. 1, an electroplating film 12 b may be deposited on anelectroless plated film 12 a formed by electroless plating, ifnecessary. The surface of the nonwoven fabric 11 is thereby covered bythe plated nickel film 12.

More specifically, the electroless plating process includes a catalyzingstep and an electroless plating step. In the catalyzing step, thenonwoven fabric is treated with an aqueous tin(II) chloride-hydrochloricacid solution and is then catalyzed with an aqueous palladium chloridesolution. Alternatively, the nonwoven fabric is directly catalyzed withan aqueous palladium solution containing a hardener with amino groups.The former process is preferred since the resulting plated film has asignificantly uniform thickness. The electroless plating is generallyperformed by reduction of nickel ions using a reducing agent in anaqueous solution containing a nickel salt, such as nickel nitrate ornickel sulfate. The plating solution may contain a complexing agent, apH modifier, a buffer and a stabilizer, if necessary. In order to form ahigh-purity nickel film, it is preferable to use a hydrazine derivative,such as hydrazine hydrate, hydrazine sulfate or hydrazine oxide, as areducing agent. In the electroless plating, for example, a long nonwovenfabric strip is continuously dipped into a catalyzing bath and then aplating bath and is wound up. Alternatively, a rolled nonwoven fabricstrip is plated by forcibly circulating a plating solution in acheese-dyeing machine. The rolled strip may be subjected to only acatalytic step or an electroless plating step, or to both steps.

Furthermore, an electroplating film 12 b is formed, if necessary, usinga plating bath. Examples of known plating baths are a Watts bath, achloride bath and a sulfamate bath. The plating bath may contain otheradditives, e.g., a pH buffer and a surfactant. A direct current or apulsed intermittent current is applied between the nonwoven fabric afterthe electroless plating as the cathode, and a nickel counter electrodeas the anode, in the bath so that the electroplating film 12 b isdeposited on the electroless plated film 12 a.

The resulting collector for alkaline secondary batteries is formed ofthe nonwoven fabric 11, which is composed of a polyolefin fiber and/or apolyamide fiber. These fibers have been used in battery separators andare reliable. Since the nonwoven fabric 11 is hydrophilized by atreatment (particularly, by sulfonation, gaseous fluorine treating, orvinyl monomer grafting), the nonwoven fabric 11 has uniform and finenegative charge over the entire region. Moreover, nickel ions are firmlyaffixed to the nonwoven fabric 11 during nickel plating. Thus, in thecollector 10, the plated nickel, film is tightly bonded to the nonwovenfabric 11, improving conductivity.

Preferably, the nonwoven fabric has a plurality of micropores extendingfrom one surface to the other surface thereof. These micropores alsoretain the active material. Since the amount of the active materialloaded into the nonwoven fabric increases, the resulting alkalinesecondary battery has high capacity. Preferably, the micropores can beformed by punching. Alternatively, the micropores may be formed by localmelting or ablation of the nonwoven fabric by heat or laser.

An alkaline secondary battery of the present invention will now bedescribed with reference to the drawings.

As shown in FIG. 2, an alkaline secondary battery 101 of the presentinvention includes the above-mentioned collector, which is hydrophilizedby a treatment (particularly, by sulfonation, gaseous fluorine treating,or vinyl monomer grafting). The battery 101 further includes a strippositive electrode 102 and a strip negative electrode 103 which are apart of this collector. The positive electrode 102 and the negativeelectrode 103 are separated by strip separators 104. These are wound upinto a roll to form an electricity-generating component 106. The battery101 has a conductive case 107 which also functions as an externalnegative electrode. The electricity-generating component 106 is loadedin the case 107. The top of the case 107 is sealed using a sealing plate108 which also functions as an external positive electrode.

The positive electrode 102 is formed as follows. A strip collector isflattened at a portion for providing a terminal, and the pores arefilled with a positive electrode paste containing a positive activematerial. A small nickel piece 102 a as an external terminal isspot-welded to the flattened portion. The negative electrode 103 isformed as follows. Another strip collector is flattened at a portion forproviding a terminal, and the pores are filled with a negative electrodepaste containing a negative active material. A small nickel piece (notshown in the drawing) as another external terminal is spot-welded to theflattened portion. The separators 104 include a first separator 104 adisposed between the positive electrode 102 and the negative electrode103 and a second separator 104 b disposed on the outer surface of thenegative electrode 103. The first and second separators 104 a and 104 b,respectively, prevent short-circuiting between the positive electrode102 and the negative electrode 103 and retain an electrolyte solution.

The case 107 is a cylinder having a bottom 107 a and the sealing plate108 seals the opening at the top of the case 107. Theelectricity-generating component 106 is placed into the case 107 so thatthe negative electrode 103 comes into contact with the inner surface ofthe case 107. The sealing plate 108 has a projection 108 a as a positiveelectrode terminal of the battery. The bottom 107 a and theelectricity-generating component 106 are isolated from each other by alower insulator 109 a. Moreover, an upper insulator 109 b is placed onthe electricity-generating component 106 in the case 107. The lowerinsulator 109 a has a slit provided for inserting the nickel piece,which is spot-welded to the negative electrode 103, while the upperinsulator 109 b has a slit provided for inserting the nickel piece 102 awhich is spot-welded to the positive electrode 102. The end of thenickel piece welded to the negative electrode 103 is connected to thebottom 107 a through the slit of the lower insulator 109 a, while theend of the nickel piece 102 a welded to the positive electrode 102 isconnected to the sealing plate 108 through the slit of the upperinsulator 109 b.

After the upper insulator 109 b is inserted into the case 107, a ringconstriction 107 b is formed at the upper portion of the case 107 in thevicinity of the case 107. The sealing plate 108 connected to the nickelpiece 102 a of the positive electrode 102 is arranged on the ringconstriction 107 b using a ring insulating packing 111 providedtherebetween. The top edge of the case 107 is folded upwardly togetherwith the insulating packing 111 so that the sealing plate 108 iselectrically insulated from the case 107 and that the case 107 is sealedby the sealing plate 108.

In such a battery 101, the first separator 104 a is laminated on theouter surface of the positive electrode 102, and then the negativeelectrode 103 and the second separator 104 b are laminated on the outersurface of the first separator 104 a. The laminate is wound into a roll.The electricity-generating component 106 is thereby fabricated. Thecollector composed of a hydrophilic nonwoven fabric coated with nickelis flexible compared to a conventional collector with a nickel networkskeleton. Thus, the positive electrode 102 and the negative electrode103 composed of the flexible collectors can be readily wound into aroll, facilitating assembly of the battery 101.

In the collector of the present invention, the plated nickel firmlyadheres to the hydrophilic nonwoven fabric. The nickel plated layer doesnot undergo a change in quality or partial scaling during assembling abattery and repeated charge/discharge cycles of the battery. Theresulting battery exhibits a high discharge rate and improvedcharge/discharge cycle characteristics compared to conventionalbatteries.

In the above embodiment, the battery is cylindrical. That is, the rolledelectricity-generating component 106 is contained in the cylindricalcase 107. The battery case may be prismatic in the present invention.The electricity-generating component may be composed of a rectangularspiral roll of the positive electrode 102 and the negative electrode 103as shown in FIG. 4, or may be composed of a folded laminate as shown inFIG. 5.

EXAMPLES

The present invention will now be described in more detail with thefollowing EXAMPLES and COMPARATIVE EXAMPLES.

Example 1

A fiber web was formed by a conventional wet process using a slurrycontaining a core-sheath composite fiber of a polypropylene core and apolyethylene sheath having a fineness of 1.2 dtex and a length of 5 mmand a solvent. The fiber web was heated to 135° C. using a drier to meltthe sheath component of the core-sheath composite fiber. The resultingnonwoven fabric had a density (per unit area) of 65 g/m², a thickness of0.5 mm and a porosity of 86%.

The nonwoven fabric was immersed into fuming sulfuric acid at 80° C. tohydrophilize the nonwoven fabric by sulfonation. The resultinghydrophilic nonwoven fabric was subjected to a nickel plating treatment.In the nickel plating treatment, the hydrophilic nonwoven fabric waswounded onto a carrier of a dyeing machine, and a scouring agent wascirculated. After the hydrophilic nonwoven fabric was washed with water,an aqueous solution containing 10 g/liter of tin(11) chloride and 20ml/liter of hydrochloric acid was circulated, followed by washing thenonwoven fabric with water. Next, an aqueous solution containing 1g/liter of palladium chloride and 20 ml/liter of hydrochloric acid wascirculated to catalyze the surface of the nonwoven fabric.

The nonwoven fabric was washed with water, and an electroless nickelsolution was circulated at 80° C. in which the plating solutioncontained 18 g/liter of nickel sulfate, 10 g/liter of sodium citrate, 50ml/liter of hydrazine hydrate, and 100 ml/liter of 25% aqueous ammonia,and the volume of the solution was determined so as to contain 55% byweight of nickel with respect to the total weight of the collector afterthe plating treatment. When the plating solution became almost clearafter one hour, the circulation was completed, and the nonwoven fabricwas washed with water and was dried to form a collector. The platednickel content of the collector, calculated from the difference inweight of the nonwoven fabric, was 50% by weight.

Example 2

A nonwoven fabric was prepared as in EXAMPLE 1. The nonwoven fabric wasintroduced into a vessel filled with a gaseous mixture of fluorine (3%by volume), oxygen (5% by volume), sulfur dioxide (5% by volume), andnitrogen (87% by volume) for 120 seconds to hydrophilize the nonwovenfabric. The hydrophilic nonwoven fabric was subjected to nickel platingas in EXAMPLE 1. The plated nickel content of the collector was 50% byweight.

Example 3

A nonwoven fabric was prepared as in EXAMPLE 1. The nonwoven fabric wassubjected to punching so that the nonwoven fabric had a plurality ofmicropores, extending from one surface to the other surface and having adiameter of 1 mm, wherein the pitch between the micropores was 8 mm andthe number thereof was about 1.5/cm². This nonwoven fabric washydrophilized as in EXAMPLE 2. The hydrophilic nonwoven fabric wassubjected to nickel plating as in EXAMPLE 1. The plated nickel contentof the collector was 50% by weight.

Example 4

A graft polymerization solution was prepared. The graft polymerizationsolution contained 30% by weight of an acrylic monomer, 0.1% by weightof benzophenone, 0.4% by weight of iron sulfate, 0.1% by weight of anon-tonic surfactant, and 69.4% by weight of water.

A nonwoven fabric was prepared as in EXAMPLE 1. The nonwoven fabric wasimmersed into the graft polymerization solution so that 0.8 weightpercent of the monomer solution was retained in the nonwoven fabric.Both surfaces of the nonwoven fabric were irradiated with ultravioletlight with a 365-nm maximum wavelength and an intensity of 180 mW/cm²for 20 seconds using two metal halide mercury lamps provided on the bothsurface to complete graft polymerization. The resulting nonwoven fabricwas washed with water and was dried. An acrylic-grafted nonwoven fabricwas prepared in such a manner. The hydrophilic nonwoven fabric wassubjected to nickel plating as in EXAMPLE 1. The plated nickel contentof the collector was 50% by weight.

Comparative Example 1

A nonwoven fabric was prepared as in EXAMPLE 1. The nonwoven fabric wasplaced into an AC corona discharging machine (made by Kasuga ElectricWorks Ltd.; electrode: aluminum Type 3) and was treated for 1 minute atan electrode distance of 2 mm, a discharge cycle of 120 times/min, afrequency of 10 kHz, and a power of 1.5 kW. The corona-treated nonwovenfabric was subjected to nickel plating as in EXAMPLE 1. The platednickel content of the collector was 50% by weight.

Comparative Example 2

A nonwoven fabric was prepared as in EXAMPLE 1. The nonwoven fabric wassubjected to nickel plating as in EXAMPLE 1 without hydrophilization.The plated nickel content of the collector was 50% by weight.

TEST 1

Regarding the collectors of EXAMPLES 1 to 4 and COMPARATIVE EXAMPLES 1and 2, the surface resistance was measured using a surface resistancemeter (LORESTA AP, made by Mitsubishi Petrochemical Co. Ltd.,) with a4-pin probe having a distance of 5 mm. Also, the surface resistance ofthe collectors, which were immersed at 60° C. into an aqueous potassiumhydroxide solution with a density of 1.3 for 10 days, were washed, andwere dried, was measured using the same apparatus.

The adhesiveness of the plated nickel to the nonwoven fabric wasmeasured by a tape peeling-off test. An adhesive tape (Nitto 31B, madeby Nitto Denko Corporation) was bonded to the surface of a collector,and was strongly pressed by a finger. One end of the tape was stretchedto peel off the tape from the collector surface. Delamination of theplated nickel from the nonwoven fabric was observed.

The tensile strength of the collector was measured using a test piecewith a width of 50 mm of the collector by a tensile tester (TensiloneUCT-500, made by Orientech Co. Ltd.). The collector was fastened by apair of chucks at a spacing of 100 m, and was stretched at a rate of 300mm/min. The tensile strength was determined by the maximum load beforethe collector was broken. These results are shown in Table 1.

TABLE 1 Tensile Adhesiveness Hydrophilic Strength Resistance (Ω)(Delamination of Plated Treatment (kg/5 cm) Initial Immersed Nickel)EXAMPLE 1 Sulfonation 16 2 × 10⁻² 2.3 × 10⁻² Not Observed EXAMPLE 2Fluorination 16 2 × 10⁻² 4.2 × 10⁻² Not Observed EXAMPLE 3 Fluorination15 2 × 10⁻² 4.2 × 10⁻² Not Observed EXAMPLE 4 Acrylic 16 2 × 10⁻² 4.4 ×10⁻² Not Observed Grafting COMPARATIVE Corona 16 2 × 10⁻²   8 × 10⁻¹Observed EXAMPLE 1 Treatment COMPARATIVE Untreated 14 2 × 10⁻² 1.2Observed EXAMPLE 2

EVALUATION 1

The results shown in Table 1 demonstrate that the adhesiveness of thecollectors after the hydrophilic treatment of the present invention(EXAMPLES 1 to 4) is superior to that of the collectors after the Coronatreatment (COMPARATIVE EXAMPLES 1 and 2), although the tensile strengthand the initial resistance are substantially the same level in all thesamples. In the hydrophilic nonwoven fabric of the present invention, acontinuous nickel film is formed by electroless plating and the platednickel is firmly affixed to the-surface of the nonwoven fabric. Incontrast, the surface modification by the corona treatment isinsufficient.

Although the sample having a plurality of micropores (EXAMPLE 3) isslightly inferior to the sample not having micropores (EXAMPLE 2) intensile strength, the tensile strength in EXAMPLE 3 is larger than 13kg/5-cm width, which is the minimum requirement for collectors.Accordingly, the collectors in EXAMPLES 1 to 4 are suitable forpractical use.

Examples of the alkaline secondary battery of the present invention willnow be described.

Examples 5

A plurality of collectors was prepared as in EXAMPLE 1. The gap portionof each collector was filled with a positive electrode paste or anegative electrode paste. Each collector was dried, was rolled, and wascut into a predetermined size. A nickel piece as an external terminalwas spot-welded to each cut collector to prepare a positive electrode ora negative electrode. Herein, the positive electrode paste contained 90percent by weight of powdered nickel hydroxide, 8 percent by weight ofpowdered carbonyl nickel as a conductive auxiliary, 2 percent by weightof powdered cobalt monoxide, carboxymethyl cellulose as a thickener, andpolytetrafluoroethylene as a tackifier. The negative electrode pastecontained a powdered hydrogen occluding alloy as a base, carboxymethylcellulose as a, thickener, and polytetrafluoroethylene as a tackifier.

Example 6

A plurality of collectors was prepared as in EXAMPLE 2. The gap portionof each collector was filled with a positive electrode paste or anegative electrode paste, which is the same as that in EXAMPLE 5. Eachcollector was dried, was rolled, and was cut into a predetermined size.A nickel piece as an external terminal was spot-welded to each outcollector to prepare a positive electrode and a negative electrode.

Example 7

A plurality of collectors was prepared as in EXAMPLE 4. The gap portionof each collector was filled with the positive electrode paste or thenegative electrode paste, which is the same as that in EXAMPLE 5. Eachcollector was dried, was rolled, and was cut into a predetermined size.A nickel piece as an external terminal was spot-welded to each cutcollector to prepare a positive electrode and a negative electrode.

Comparative Example 3

A polyurethane foam sheet having a porous network skeleton was subjectedto known nickel plating, and was fired in a reducing atmosphere topyrolyze the polyurethane resin while remaining the plated nickelnetwork skeleton. A plurality of collectors with three-dimensionalnetwork structures was prepared in such a manner. The gap portion ofeach collector was filled with a positive electrode paste or a negativeelectrode paste, which was the same as that in EXAMPLE 5. Each collectorwas dried, was rolled, and was cut into a predetermined size. A nickelpiece as an external terminal was spot-welded to each cut collector asin EXAMPLE 5 to prepare a positive electrode and a negative electrode.

Comparative Example 4

A plurality of collectors having the same structure as that inCOMPARATIVE EXAMPLE 2 was prepared as in COMPARATIVE EXAMPLE 2. The gapportion of each collector was filled with a positive electrode paste ora negative electrode paste, which was the same as that in EXAMPLE 5.Each collector was dried, was rolled, and was cut into a predeterminedsize. A nickel piece as an external terminal was spot-welded to each cutcollector to prepare a positive electrode and a negative electrode.

Comparative Example 5

A plurality of collectors having the same structure as that inCOMPARATIVE EXAMPLE 1 was prepared as in COMPARATIVE EXAMPLE 1. That is,nonwoven fabrics were subjected to nickel plating without a hydrophilictreatment. The gap portion of each collector was filled with a positiveelectrode paste or a negative electrode paste, which was the same asthat in EXAMPLE 5. Each collector was dried, was rolled, and was cutinto a predetermined size. A nickel piece as an external terminal wasspot-welded to each cut collector to prepare a positive electrode and anegative electrode.

TEST 2

A plurality of cylindrical battery cases with a Sub-C size and aplurality of prismatic battery cases of 6.1 mm by 17.0 mm by 67.0 mm inouter sizes were prepared. A melt-type nonwoven fabric separator of acore-sheath composite fiber composed of a polypropylene core and apolyethylene sheath was prepared. Any one of the positive electrodes andany one of the negative electrodes in EXAMPLES 5 and COMPARATIVEEXAMPLES 3 and 4 were selected and were laminated with the separatortherebetween to form laminates. Laminates were wound into a spiral rollas shown in FIG. 3, a rectangular spiral roll as shown in FIG. 4, and afolded laminate as shown in FIG. 5 to form electricity-generatingcomponents. Each electricity-generating component was inserted into acylindrical or prismatic battery case. The negative-electrode externalterminal was welded to the bottom of the battery case, which functionsas a negative electrode. After the battery case was necked, apredetermined amount of alkaline electrolyte solution was placedtherein. The top of the case was sealed with a sealing plate, which alsofunctions as a positive terminal, to complete an alkaline secondarybattery. Twenty-seven alkali secondary batteries having a rated capacityof 2,500 mAh or 1,300 mAh were fabricated in such a manner. The internalresistance of each battery was measured. Table 2 shows the capacities ofthe positive electrode and the negative electrode and the combinationthereof, the shape and the weight energy density of theelectricity-generating component, the type of the battery case, and theobserved internal resistance in each of the twenty-seven alkalisecondary batteries.

TABLE 2 Positive Electrode Negative Electrode Electricity-generatingComponent Capacity Capacity Energy Density Internal Battery Type (mAh)Type (mAh) Shape (Wh/kg) Shape of Case Resistance (mΩ) 1 EXAMPLE 5 2,452EXAMPLE 5 3,457 Spiral 134 Cylinder 15.3 2 1,248 1,843 RS(*1) 128 Prism14.6 3 1,347 1,887 Folded 137 Prism 14.8 4 EXAMPLE 5 2,537 COMPARATIVE3,561 Spiral 106 Cylinder 16.1 5 1,260 EXAMPLE 3 1,801 RS(*1) 103 PrismISC(*2) 6 1,308 1,857 Folded 102 Prism ISC(*2) 7 EXAMPLE 5 2,538COMPARATIVE 3,576 Spiral 118 Cylinder 23.6 8 1,248 EXAMPLE 4 1,769RS(*1) 124 Prism 25.3 9 1,339 1,882 Folded 120 Prism 24.9 10 COMPARATIVE2,553 EXAMPLE 5 3,599 Spiral 110 Cylinder 16.4 11 EXAMPLE 3 1,309 1,846RS(*1) 104 Prism ISC(*2) 12 1,314 1,853 Folded 108 Prism ISC(*2) 13COMPARATIVE 2,439 EXAMPLE 5 3,485 Spiral 120 Cylinder 37.6 14 EXAMPLE 41,276 1,848 RS(*1) 118 Prism 38.2 15 1,293 1,901 Folded 121 Prism 36.916 COMPARATIVE 2,452 COMPARATIVE 3,457 Spiral 94 Cylinder 15.1 17EXAMPLE 3 1,262 EXAMPLE 3 1,779 RS(*1) 93 Prism ISC(*2) 18 1,305 1,844Folded 95 Prism ISC(*2) 19 COMPARATIVE 2,537 COMPARATIVE 3,654 Spiral105 Cylinder 23.8 20 EXAMPLE 3 1,356 EXAMPLE 4 1,954 RS(*1) 109 PrismISC(*2) 21 1,308 1,839 Folded 108 Prism ISC(*2) 22 COMPARATIVE 2,538COMPARATIVE 3,564 Spiral 103 Cylinder 37.9 23 EXAMPLE 4 1,360 EXAMPLE 31,918 RS(*1) 110 Prism ISC(*2) 24 1,337 1,880 Folded 103 Prism ISC(*2)25 COMPARATIVE 2,553 COMPARATIVE 3,625 Spiral 118 Cylinder 42.8 26EXAMPLE 4 1,275 EXAMPLE 4 1,838 RS(*1) 125 Prism 43.1 27 1,264 1,770Folded 126 Prism 44.0 (*1)Rectangular Spiral; (*2)InternalShort-circuiting

TEST 3

Batteries 1, 4, 7, 10, 13, 16, 19, 22, and 25 used in TEST 2 wereprepared. Each battery was charged for 6 hours at a charge rate C/5,wherein C was the capacity of the battery, and was allowed to stand for1 hour. Next, the battery was discharged at a discharge rate of 10Cuntil the voltage became 0.8 V to measure the discharge capacity C1 atthis time. The high-rate discharge characteristic R1 represented by theratio C/C1 was thereby determined.

Furthermore, each battery was charged for 6 hours at a charge rate C/5and was allowed to stand for 1 hour. The battery was discharged at 400mAh until the voltage became 0.9 V. This charge/discharge operation wasrepeated 500 times to determine the high-rate discharge characteristicR2 represented by C₅₀₀/C_(MAX) wherein C₅₀₀ was the discharge capacityat the 500th cycle and C_(MAX) was the maximum discharge capacity in the500 cycles.

Table 3 shows the high-rate discharge characteristics R1 and R2.

TABLE 3 Positive Negative Battery Electrode Electrode R1 R2 1 EXAMPLE 5EXAMPLE 5 87 91 4 EXAMPLE 5 COMPARATIVE 86 90 EXAMPLE 3 7 EXAMPLE 5COMPARATIVE 49 10 EXAMPLE 4 10 COMPARATIVE EXAMPLE 5 88 92 EXAMPLE 3 13COMPARATIVE EXAMPLE 5 50 12 EXAMPLE 4 16 COMPARATIVE COMPARATIVE 88 89EXAMPLE 3 EXAMPLE 3 19 COMPARATIVE COMPARATIVE 48 13 EXAMPLE 3 EXAMPLE 422 COMPARATIVE COMPARATIVE 49 14 EXAMPLE 4 EXAMPLE 3 25 COMPARATIVECOMPARATIVE 20 Undischarged EXAMPLE 4 EXAMPLE 4

TEST 4

A plurality of cylindrical battery cases with a Sub-C size was prepared.A melt-type nonwoven fabric separator of a core-sheath composite fibercomposed of a polypropylene care and a polyethylene sheath was preparedto form positive electrodes in EXAMPLES 5, 6, and 7 and COMPARATIVEEXAMPLES 4 and 5 and negative electrodes in COMPARATIVE EXAMPLE 3. Eachof the positive electrodes and the negative electrodes was laminatedwith a separator therebetween, and each laminate was coiled as shown inFIG. 3 to form an electricity-generating component. Theelectricity-generating component was inserted into the cylindricalbattery case. The negative-electrode external terminal was welded to thebottom of the battery case, which functions as a negative electrode.After the battery case was necked, a predetermined amount of alkalineelectrolyte solution was placed therein to prepare five alkalinesecondary batteries (Batteries 28 to 32).

Each battery was charged for 6 hours at a charge rate C/5 and wasallowed to stand for 1 hour wherein C was the capacity of the battery.The battery was discharged at 400 mAh until the voltage became 0.9 V.This charge/discharge cycled operation was repeated 500 times. Thenumber of the repeated cycles when the discharge capacity decreased to80% of the maximum discharge capacity C_(MAX) among the 500 dischargecapacities was defined as the cycle life of the battery. Table 4 showsthe cycle life and the internal resistance when the cycle life wasdetermined.

TABLE 4 Internal Positive Negative Resistance Battery ElectrodeElectrode Cycle Life (mΩ) 28 EXAMPLE 5 COMPARATIVE >500 16.1 EXAMPLE 3cycles 29 EXAMPLE 6 COMPARATIVE >500 18.8 EXAMPLE 3 cycles 30 EXAMPLE 7COMPARATIVE >500 19.5 EXAMPLE 3 cycles 31 COMPARATIVE COMPARATIVE 27035.5 EXAMPLE 4 EXAMPLE 3 32 COMPARATIVE COMPARATIVE 230 37.9 EXAMPLE 5EXAMPLE 3

EVALUATION 2

Table 2 shows that all the batteries including the rectangular spiralelectricity-generating components or the folded electricity-generatingcomponents formed of the positive or negative electrode in EXAMPLE 3 areinternally short-circuited. The reason for this phenomenon is presumedas follows. The nickel itself constituting the network skeleton is lessflexible in the electrode in COMPARATIVE EXAMPLE 3. When a laminateincluding this electrode is wound up or folded, the network skeleton ofthe collector breaks. As a result, the network skeleton has cracks andprojections producing scuffing on the outer periphery of the electrodeusing this collector, due to chipping of the electrode collector. Theseprojections break through the separator and cause short-circuiting.

Table 3 shows that the batteries including the positive electrode or thenegative electrode in COMPARATIVE EXAMPLE 4 exhibit high-rate dischargecharacteristics and cycle characteristics which are inferior to those ofthe other batteries. Battery 25 using the positive electrode and thenegative electrode of COMPARATIVE EXAMPLE 4 is undischargeable beforethe completion of the 500 cycles. The reason for this phenomenon ispresumed as follows. Since the nonwoven fabric is plated with nickelwithout a hydrophilic treatment in the electrode in COMPARATIVE EXAMPLE4, the adhesion of the plated nickel to the nonwoven fabric isinsufficient. The plated nickel layer undergoes a change in quality orpartial scaling from the nonwoven fabric during assembling a battery andrepeated charge/discharge cycles of the battery.

In contrast, Table 2 shows that all the batteries including theelectricity-generating components formed of the positive electrode orthe negative electrode in EXAMPLES 5 and not causing internalshort-circuiting exhibit low internal resistance and satisfactorycollecting functions in all the battery shapes compared to the otherbatteries. Moreover, Table 3 shows that all the batteries including theelectricity-generating components formed of the positive electrode andthe negative electrode in EXAMPLE 5 are superior in high-rate dischargecharacteristics and cycle characteristics compared to the otherbatteries. The reason is presumed as follows. The collector of thepresent invention is more flexible compared to that in COMPARATIVEEXAMPLE 3 and exhibits adequate adhesiveness between the plated nickelfilm and the nonwoven fabric compared to that in COMPARATIVE EXAMPLE 4.

Table 4 shows that the batteries including the electricity-generatingcomponents formed of the positive electrodes in COMPARATIVE EXAMPLES 4and 5 exhibit cycle characteristics inferior to those of the otherbatteries. As evidently shown in TEST 1, these results are presumablydue to the delamination of the plated film by the alkaline electrolytesolution in the battery or an increased internal resistance due to theincreased surface resistance of the collector.

According to the present invention, as described above, a nonwovenfabric comprising at least one of a polyolefin fiber and a polyamidefiber is hydrophilized, and the hydrophilic nonwoven fabric is platedwith nickel. Thus, the hydrophilic nonwoven fabric has a uniform andfine negative charge over the entire region due to improvedpenetrability of a plating solution. Thus, nickel ions are firmlyaffixed to the surface of the nonwoven fabric in a nickel platingtreatment, the plated nickel layer tightly bonded to the nonwovenfabric. The resulting collector exhibits high conductivity.

Since the nonwoven fabric has a plurality of micropores extending fromone surface to the other surface thereof, a large amount of activematerial is loaded into the plurality of micropores, so that thealkaline secondary battery using this collector has high capacity.

Since the nonwoven fabric including crimped fibers is bulky, it can loadan increased amount of active material, resulting in an increase incapacity of the alkaline secondary battery. Moreover, the average porevolume increases; hence a further increased amount of active materialcan be loaded. Since the nonwoven fabric prepared by a wet process isuniform with regard to area weight and thickness, a uniform electrode isobtainable. Thus, an electrode with a uniform thickness can be formedusing this collector. When this electrode is wound up, an electrodegroup having high adhesiveness is formed, and a battery using the woundelectrode exhibits superior charge/discharge characteristics.

Since the surface of the nonwoven fabric is hydrophilized bysulfonation, gaseous fluorine treating, or vinyl monomer grafting, thequality of the resulting collector is stable. When the nickel plating iselectroless plating, the electroless plating facilitates the formationof a stable nickel film on the nonconductive nonwoven fabric. When anelectroplating film is formed by an electroplating process subsequent tothe formation of an electroless plating film by the electroless plating,the plated nickel film having a predetermined thickness is tightlybonded to the nonwoven fabric, and the resulting collector has desiredconductivity.

In addition, an alkaline secondary battery can be readily assembledusing the above-mentioned collector, and exhibits a high discharge rateand improved charge/discharge cycle characteristics due to highadhesiveness of the collector to the plated nickel layer.

What is claimed is:
 1. A method for making a collector for an alkalinesecondary battery, comprising: a hydrophilizing step of hydrophilizing anonwoven fabric comprising at least one of a polyolefin fiber and apolyamide fiber to produce a hydrophilic nonwoven fabric; and a platingstep of applying nickel plating to the hydrophilic nonwoven fabric,wherein said hydrophilizing step includes a treatment selected from thegroup consisting of sulfonation and gaseous fluorine treating.
 2. Amethod for making a collector for an alkaline secondary batteryaccording to claim 1, wherein the nonwoven fabric has a plurality ofmicropores extending from one surface to the other surface thereof.
 3. Amethod for making a collector for an alkaline secondary batteryaccording to claim 1, wherein the nickel plating step compriseselectroless plating.
 4. A method for making a collector for an alkalinesecondary battery according to claim 2, wherein the nickel plating stepcomprises electroless plating.
 5. A method for making a collector for analkaline secondary battery according to claim 3, wherein the step ofelectroless plating produces an electroless plating film.
 6. A methodfor making a collector for an alkaline secondary battery according toclaim 4, wherein the step of electroless plating produces an electrolessplating film.